Madrid face Real Mallorca on Saturday night looking to extend their lead to eight points before Barca take on Real Betis at home on Sunday.
They do so digesting the news they will meet their great rivals in the quarter-finals of the Copa del Rey, however, after both progressed in their ties this week.
Goalkeeper Casillas is relishing the chance to square off with Barca but maintains the league must be their immediate priority.
"We shouldn't obsess about the tie," he told realmadrid.com. "It will be beautiful. Draws are somewhat capricious and we're going to wait.
"Our minds are set on Mallorca.
"The less (we play Barcelona) the better because too much of one thing can be exhausting. We played four games against Barcelona in a short time last year and the same may happen again this season.
"We'll try to do well in both games to reach the next round. It happens so often that it seems to be deprived of its own thrill aspect. They did better last time, but that changes from one day to the next. We'll take a further step forward if we win the league title and reach the Champions League final, but we know it won't be easy."
Madrid will have to do without Germany midfielder Sami Khedira at Son Moix after he suffered a sprained ankle against Malaga which is set to sideline him for a month. Angel Di Maria, meanwhile, may require a late fitness test on a knock.
Casillas' counterpart, Mallorca goalkeeper Dudu Aouate, knows the size of the task facing his team.
"Real Madrid surpass us in terms of quality and we must work together to give everything. We have faith in ourselves that we can do something beautiful.
"They are a very strong team that is in good form and are ahead of Barcelona by five points. But the best team does not always win."
However, Aouate is wary of the direct threat he could face from Cristiano Ronaldo, Gonzalo Higuain and Karim Benzema.
"Cristiano is very good, one of the best and he's almost scored a goal per game. I have no doubt, as a goalkeeper, that he's one of the best. But I'm not afraid, I've had many years in the Spanish league and I've stopped some of the best strikers.
"Cristiano is a player who knows how to hit the ball with more power while Higuain is one of the most dangerous strikers I've come across. Then there is Benzema, who is doing a great job."
Mallorca boss Joaquin Caparros welcomed striker Marvin Ogunjimi back to training this week after an ankle injury following his arrival from Genk and he could finally make his La Liga debut.